1. Field of the Invention
The present invention relates to the preparation of a mixture containing cyclohexanol and cyclohexanone from cyclohexane.
More especially, this invention relates to a process in which cyclohexane is oxidized in the presence of air to form a mixture containing cyclohexyl hydroperoxide, hereinafter referred to as CHHPO, such hydroperoxide then being decomposed. The principal products formed during the decomposition are cyclohexanol (OL) and cyclohexanone (ONE). These compounds are converted by oxidation into adipic acid, one of the main starting materials in the production of polyamides. Cyclohexanone is also an intermediate for producing caprolactam, a compound used in the manufacture of certain polyamides.
2. Description of the Prior Art
D. Mansuy and his co-workers have described, in Angew. Chem., Int. Ed. Engl., 19, No. 11, pages 909-910 (1980), the oxidation of cyclohexane with cumyl hydroperoxide, in the presence of the complex: EQU Mn.sup.III (TPP)Cl,
wherein TPP is tetraphenylporphyrin.
However, the yields remain low, and the catalyst is expensive and sensitive to oxygen. Additionally, it is essential to conduct the reaction in the presence of a solvent.
Although French Pat. No. 1,263,449 describes the decomposition of cyclohexyl hydroperoxide in a mixture resulting from the oxidation of cyclohexane, prior to the separation of the latter, in the presence of a manganese and copper combination which can be dispersed in the reaction mixture, this is a total decomposition. However, the cyclohexane is not oxidized.
Moreover, an improved process for the oxidation of cyclohexane to form a reaction mixture containing CHHPO and for the decomposition of such hydroperoxide in the presence of cyclohexane (starting material) to form a mixture containing cyclohexanol and cyclohexanone is described in published European Patent Application No. EP-A-0,027,937. This improved process features the use of a complex of a transition metal and compounds of the 1,3-bis(pyridylimino)isoinodoline group as catalyst in the oxidation and/or decomposition stage.
An important aspect of this process resides in the participation of the cyclohexane, namely, a higher conversion of said cyclohexane into "useful" oxidation products than that which would normally be observed during the decomposition of CHHPO alone.
However, this process has two major disadvantages: firstly, the use of ligands which are very expensive and/or difficult to prepare and secondly, the sensitivity of such ligands to oxidizing agents.